The present invention relates to somatic mutations of the neurofibromatosis type 1 (NF1) gene in human tumors. The invention further relates to methods for the detection and treatment of humans having somatic mutations in the NF1 genes in tumors.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting its practice, are incorporated by reference herein and for convenience are numerically referenced in parentheses in the following text and respectively grouped in the appended bibliography.
The neurofibromatoses are genetic disorders that primarily affect cell growth of neural tissues. These disorders can cause tumors to grow on the nerves at any location and at any time. Some manifestations are progressive, and may result in significant morbidity or mortality. Two distinctive forms are recognized, but variant forms may exist.
The most common type, neurofibromatosis type 1 or NF1 (previously known as yon Recklinghausen's neurofibromatosis or peripheral neurofibromatosis), is an autosomal dominant disorder affecting about 1 in 3,500 individuals (1). It has been found that the spontaneous mutation rate is quite high, with 30%-50% of NF1 affected individuals representing new mutations. This leads to a calculated mutation rate of about 1/10,000, which is about 100-fold higher than the usual mutation rate for a single locus. One explanation for such a high mutation rate is that the NF1 gene is a megagene which has been confirmed by its cloning and sequencing.
The clinical features of the disorder are startlingly variable, even within the same family, indicating that other events must play a role in the eventual phenotype of the disease. The diagnostic criteria for NF1 include the presence of two or more of the following: (1) six or more cafe-au-lait macules more than 15 mm in greatest diameter in postpubertal individuals, or 5 mm in prepubertal individuals; (2) two or more neurofibromas of any type, or one plexiform neurofibroma; (3) freckling in the axillary or inguinal regions; (4) optic glioma; (5) two or more Lisch nodules (iris hamartomas); (6) a distinctive bony lesion such as sphenoid dysplasia or thinning of long-bone cortex, with or without pseudoarthrosis; (7) a first-degree relative with NF1 (1). The penetrance of NF1 is extremely high if individuals are carefully examined, including use of a slit-lamp to detect Lisch nodules. Under those circumstances, it is rare to identify an adult obligate gene carrier who does not meet the criteria listed above (2).
The NF1 gene has been identified (3-6). Analysis of the NF1 gene product, neurofibromin, demonstrated that neurofibromin contains a domain showing approximately 30% similarity to the catalytic domains of yeast IRA1 and IRA2 proteins and the mammalian GTPase are activating protein (GAP) (7,8). The yeast IRA genes encode negative regulators of yeast RAS genes that are homologs of mammalian GAP (9-11).
Guanine nucleotide binding to ras proteins mediates signal transduction that regulates cell growth: binding to GTP activates signaling, while hydrolysis to GDP terminates signaling (12). A GTPase-activating protein (GAP) was the first protein found to catalyze the hydrolysis to GDP and thereby mediate the signal termination event (13). In addition to this role, it has been proposed that GAP may also function in signal propagation as a downstream effector of ras (14,15). More recently, the GAP-related domain (GRD) of neurofibromin, the neurofibromatosis 1 (NF1) gene product, was also found to stimulate the GTPase of ras (8,16,17) and to possess properties consistent with the functioning of neurofibromin as a downstream effector of ras (18).